Itching is a common symptom in dermatologic diseases and causes restless scratching of the skin. We have previously shown by using an in vivo patch-clamp technique that pruritic synaptic responses are evoked in spinal dorsal horn (SDH) neurons of rats. Topically application of 5-HT to the rat skin increased the frequency of the large amplitude of spontaneous EPSCs in about 30 % of the neurons recorded. In this study, we examined the electrophysiological characteristics (mainly firing patterns) of the SDH neurons receiving 5-HT-sensitive afferent fibers. In current-clamp mode, current pulses were applied to SDH neurons to elicit action potentials. SDH neurons tested were classified into five types based on their firing patterns: delayed firing, tonic firing, phasic firing, initial firing and other firing. Most (about 70%) of the 5-HT-responsive neurons were the delayed and tonic firing types, although 5-HT-unresponsive neurons were also found in these two types of SDH neurons. The relationship between the morphological class of SDH neurons and their firing patterns has previously shown that vertical cells exhibit the delayed or tonic firing type. Moreover, central cells are reported to exhibit the initial firing pattern of discharge. In combination with the previous studies, the present results suggest that pruriceptive afferent fibers evoke excitatory synaptic responses mainly onto delayed firing and tonic firing type neurons which are morphologically classified as the vertical cell.